libct/nsenter: save errno in sane_kill

Since sane_kill after a failed read or write, but before reporting the
error from that read or write, it may change the errno value in case
kill(2) fails.

Save and restore the errno around the call to kill.

Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

libcontainer/nsenter/nsexec.c

@@ -639,9 +639,14 @@ void join_namespaces(char *nsspec)
 
 static inline int sane_kill(pid_t pid, int signum)
 {
-	if (pid > 0)
-		return kill(pid, signum);
-	else
+	if (pid > 0) {
+		int ret, saved_errno;
+
+		saved_errno = errno;
+		ret = kill(pid, signum);
+		errno = saved_errno;
+		return ret;
+	} else
 		return 0;
 }